1. Field of the Invention
This invention relates to textile drying appliances (e.g., dryers), and more specifically to dryers used to dry garments associated with the semiconductor industry subsequent to cleaning the garments in a fluid (e.g., water) which is absorbed by the clean room garments.
2. Description of Related Art
It is well known that small particles (i.e., particulates) can cause defects in integrated circuits formed upon semiconductor wafers. Such defects may prevent the integrated circuits from performing their intended functions. For example, a process called photolithography is used to pattern layers of desired materials deposited upon the semiconductor wafers. During photolithography, light passing through a pattern on a mask transfers the pattern to a layer of light-sensitive photoresist deposited over the layer of the desired material. Particulates on the surface of the mask or on the surface of the photoresist layer which block or diffuse the light cause imperfect pattern registrations (i.e., imperfect feature formations). Such imperfect features formed within an integrated circuit may render the integrated circuit inoperable.
In order to help keep wafer processing areas as particle free (i.e., "clean") as possible, such areas are designated as "clean rooms". Particulates may be present within the air in clean rooms, introduced by processing personnel, suspended in liquids and gasses used during wafer processing, and generated by processing equipment located within the clean rooms. As a result, the air within clean rooms is typically continuously filtered. Liquids and gasses entering clean rooms and used during processing are also filtered, and clean rooms typically exclude portions of processing equipment which generate particulates.
Air "cleanliness" levels of clean rooms are determined by the densities of different sizes of particulates present in the air and are specified using class numbers. The allowable densities of particulates within clean rooms is dependent upon the clean room class numbers and the largest dimensions of the particulates. For example, a class 1 clean room can have only 1 particle with a largest dimension of 0.5 micron in each cubic foot of air, but may have up to 34 particles with largest dimensions of 0.1 micron per cubic foot of air. The required class number for a particular clean room is largely determined by the feature sizes of the integrated circuit devices being produced within the clean room. Portions of many integrated circuits produced today are formed within class 1 clean rooms.
Human beings continuously generate large numbers of particulates including dead skin cells and hairs. When working in clean rooms, personnel typically wear low-particle-generating coverings which almost completely envelope their bodies. The clean room garments essentially form filters around the wearers, reducing the number of particulates generated by the wearers which escape into the air. Exemplary garments include overalls and hoods, face masks, safety glasses or goggles, leggings, shoe covers, and gloves. Undergarments such as caps or nets may also be used to keep hair in place under hoods.
In a typical clean room, filtered air is supplied from the ceiling and return air is drawn through a perforated floor, providing a continuous vertical laminar flow of filtered air. Particles released by clean room personnel and equipment are hopefully swept downward by the laminar flow of air before coming to rest upon surfaces of wafers or processing equipment.
Clean room garments must be laundered on a regular basis if they are to remain serviceable. Laundering clean room garments at an off-site facility presents a problem in that particles may be introduced into the garments during transport through the relatively "dirty" environment between the off-site facility and the clean room. In fact, the plastic bags routinely used to protect laundered garments are themselves particle generators, rendering them ineffective in protecting clean room garments from the introduction of particles during transit. One way of solving the problem of particle introduction during transport is to eliminate the need for transport by laundering the clean room garments in a laundering facility located within or adjacent to the clean room.
Problems arises when laundering clean room garments in a facility located within or adjacent to the clean room. Textile drying appliances (i.e., "dryers") typically operate by facilitating the vaporization (i.e., evaporation) of a liquid (e.g., water) within textiles (e.g., garments) placed within the dryers. The dryers continuously exhaust the vapor-laden air surrounding the textiles and draw in relatively vapor-free "makeup" air. The vapor-laden air is typically exhausted to an exterior space, and the makeup air is typically drawn from the room in which the dryers are located. Relatively large volumes of air drawn from a laundering room located within or adjacent to a clean room may create a vacuum which disrupts the vertical laminar flow of air within the clean room. This disruption in the vertical laminar flow of air may result in an increase in the number of particulates causing wafer defects.
It would thus be desirable to have a textile drying system which does not draw air from, or provide air to, a room in which the textile drying system is located. When located within or adjacent to a clean room, such a textile drying system would not create a vacuum which may disturb a vertical laminar flow of air within the clean room. The desired textile drying system would thus be suitable for installation in a laundry room located within or adjacent to the clean room.